The present invention relates in general to polymers, and in particular to a new a useful method and composition for modifying the impact characteristics of polymers.
The impact modification of polymers is possible through incorporation of rubbery phase domains into an otherwise brittle polymer matrix. High impact polystyrene (HIPS), acrylonitrile-butadiene-styrene (ABS), and modified epoxies are well-known and important materials that employ this technique. The size of the rubber phase domains in many cases determines the degree of toughening that occurs in a particular system.
Two phase rubber/polymer blends have been produced by a number of methods. These methods include mechanical blending, precipitation polymerization, emulsion polymerization, and block copolymerization. These existing processes have limitations and cannot always be used to produce the desired micro-dispersion. See Nauman, E. B., et al., Chem. Eng. Comm., 66, 29 (1988).
A new process called compositional quenching, has been developed in which a blend of finely dispersed rubbery phase within a continuous polymer phase can be created by rapid removal of the solvent from a single phase polymer solution. As the solvent is being removed, phase separation occurs by spinodal decomposition. The size of the rubber phase domain is, in part, a function of the rate of solvent removal. High rates of solvent removal produce very small particles. See Nauman, S. and Strella, S., J. Appl. Poly. Sci., 9, 2297-2310 (1965), and Bucknall, C. B. "Toughened Plastics", Applied Science, London, (1977), as well as U.S. Pat. Nos. 4,594,371 and 4,666,961 to Nauman.
A high-temperature polyetherimide, sold under the tradename ULTEM 1000 (ULTEM is a registered trademark of the General Electric Company) is in a group of polymers which are particularly interesting for military, electronic, and automotive applications, where thermal stability is important. Most heat-resistant polymers are quite brittle, however. This brittleness is often due to the stiff polymer backbone that also imparts the high thermal stability. It is difficult to alter the polymer backbone to add toughness without adversely affecting thermal stability.